Laryngospasm

Laryngospasm is involuntary, sustained closure of the vocal cords and false cords, obstructing the airway during anaesthesia. It is partial (stridor) or complete (silent, with paradoxical chest and abdominal movement).

Epidemiology. It affects about 1% of anaesthetics, about 1.7% in children, and up to 10% to 25% in young children with a recent respiratory infection. It is a leading cause of perioperative hypoxaemia.

Risk factors. Light anaesthesia, airway stimulation (secretions, blood, suction, airway insertion or removal), recent upper respiratory infection (within 2 to 4 weeks), asthma, smoking, reflux, young age, ENT surgery, desflurane and extubation at a light plane.

Complications. Hypoxaemia, bradycardia, negative pressure pulmonary oedema, aspiration, regurgitation and cardiac arrest.

Pathophysiology.

Stimulation of superior laryngeal nerve afferents triggers a brainstem reflex that contracts the adductor muscles (lateral cricoarytenoid, thyroarytenoid and cricothyroid). Light anaesthesia and hypoxaemia lower the threshold.

Crowing stridor then silence, rocking chest and abdomen, tracheal tug, no breath sounds, loss of capnography trace, desaturation, bradycardia, and cyanosis.

Red flags.

• Complete obstruction with silent chest.
• Saturation under 90%.
• Bradycardia, especially in children.
• Pink frothy sputum (negative pressure oedema).
• Loss of cardiac output.

Clinical. Confirm the lost trace on capnography and absence of gas flow. Exclude a blocked tube or circuit.

Differential diagnosis.

• Bronchospasm.
• Foreign body or secretions.
• Tongue obstruction.
• Opioid induced chest wall rigidity.
• Anaphylaxis.
• Vocal cord paralysis.
• Laryngeal oedema.
• Tension pneumothorax.

Stop all stimulation and suction only under direct vision. Give 100% oxygen, perform a jaw thrust, and apply continuous positive airway pressure of 10 to 20 cmH2O by tight fitting mask. Apply firm pressure bilaterally behind the ear lobule at the laryngospasm notch (Larson manoeuvre).

• Propofol: 0.25 to 0.8 mg/kg IV, repeated once if needed; maximum 1 mg/kg total for this indication; monitor blood pressure, heart rate and airway; reduce in older adults and hypovolaemia.
• Succinylcholine (if hypoxaemia persists or the airway is lost): adults 0.1 to 0.5 mg/kg IV (about 20 to 40 mg); children 0.5 to 1 mg/kg IV, or 4 mg/kg IM if there is no IV; single dose; maximum 1 mg/kg IV; monitor ECG, heart rate and ventilation; avoid in burns, denervation, myopathy and hyperkalaemia; give atropine first in children; prolonged by plasma cholinesterase deficiency.
• Atropine (before a repeat succinylcholine dose or for bradycardia): adults 500 microgram IV, children 20 microgram/kg IV (minimum 100 microgram, maximum 500 microgram each dose); repeat every 3 to 5 minutes; maximum 3 mg in adults; monitor heart rate; use caution in glaucoma and tachyarrhythmia.
• Rocuronium (if succinylcholine is contraindicated): 0.6 to 1.2 mg/kg IV once; maximum 1.2 mg/kg; monitor train-of-four; sugammadex available.

Ventilate with oxygen after relaxation, and intubate if needed. Treat bradycardia and arrest by the advanced life support algorithm.

Prevention.

• Extubate fully awake, or at a deep plane with an experienced operator, after gentle suction under vision.
• Avoid desflurane in at risk patients, and delay elective paediatric surgery for 2 to 4 weeks after a respiratory infection.
• Lidocaine: 1 to 1.5 mg/kg IV 1 to 2 minutes before extubation, single dose; maximum 3 mg/kg; monitor ECG and symptoms of toxicity; reduce in hepatic impairment, heart failure and heart block.

Monitoring. Saturation, capnography and chest examination for at least 30 minutes after a severe episode, with observation for pulmonary oedema.

Referral and escalation. Senior anaesthetic help for persisting obstruction. ENT review for recurrent episodes, and critical care for pulmonary oedema or arrest.

Special groups. Children are most vulnerable and desaturate quickly. Patients with reflux or recent infection need deeper anaesthesia or awake extubation.